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Branches的Merge操作</a></li><li class="dropdown-item"><!----> <a href="/pages/0c0ca8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端学习" class="dropdown-title"><!----> <span class="title" style="display:;">前端学习</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/99897f/" class="nav-link">HTML与CSS</a></li><li class="dropdown-item"><!----> <a href="/pages/51542d/" class="nav-link">JS学习</a></li><li class="dropdown-item"><!----> <a href="/pages/803f9d/" class="nav-link">Vue3入门</a></li><li class="dropdown-item"><!----> <a href="/pages/ca4cfb/" class="nav-link">Vue3进阶</a></li><li class="dropdown-item"><!----> <a href="/pages/50e8d3/" class="nav-link">黑马Vue3</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="MFC" class="dropdown-title"><!----> 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class="dropdown-item"><!----> <a href="/pages/28ec23/" class="nav-link">NAND Flash</a></li><li class="dropdown-item"><!----> <a href="/pages/62bf40/" class="nav-link">ARM 处理器</a></li><li class="dropdown-item"><!----> <a href="/pages/1a9374/" class="nav-link">嵌入式基础知识-存储器</a></li><li class="dropdown-item"><!----> <a href="/pages/aac5e3/" class="nav-link">闪存存储和制造技术概述</a></li><li class="dropdown-item"><!----> <a href="/pages/8f6056/" class="nav-link">芯片IO驱动力</a></li><li class="dropdown-item"><!----> <a href="/pages/d146b8/" class="nav-link">主流先进封装技术介绍</a></li><li class="dropdown-item"><!----> <a href="/pages/16f0ba/" class="nav-link">NAND Flash基础</a></li><li class="dropdown-item"><!----> <a href="/pages/90d8d0/" class="nav-link">基于PA算法的FTL引导</a></li><li class="dropdown-item"><!----> <a href="/pages/eb672b/" class="nav-link">SD逻辑擦除和物理擦除</a></li><li class="dropdown-item"><!----> <a href="/pages/747121/" class="nav-link">NAND Flash的SDR、ONFI、DDR接口</a></li><li class="dropdown-item"><!----> <a href="/pages/1eb351/" class="nav-link">【详解】Nand Flash必看知识</a></li><li class="dropdown-item"><!----> <a href="/pages/d2512a/" class="nav-link">【两万字详解】Nand Flash必看知识</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="面经" class="dropdown-title"><!----> <span class="title" style="display:;">面经</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d69946/" class="nav-link">虎牙C++技术面经</a></li><li class="dropdown-item"><!----> <a href="/pages/29251d/" class="nav-link">金山一面复习</a></li><li class="dropdown-item"><!----> <a href="/pages/c7c01f/" class="nav-link">完美世界秋招 C++ 游戏开发面经(Cpp部分)</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="其它" class="dropdown-title"><!----> <span class="title" style="display:;">其它</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/fa256e/" class="nav-link">博客搭建</a></li><li class="dropdown-item"><!----> <a href="/pages/335531/" class="nav-link">网站收藏箱</a></li></ul></div></div> <!----></nav></div></header> <div class="sidebar-mask"></div> <div class="sidebar-hover-trigger"></div> <aside class="sidebar" style="display:none;"><!----> <nav class="nav-links"><div class="nav-item"><a href="/" class="nav-link">首页</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="CPP语言" class="dropdown-title"><!----> <span class="title" style="display:;">CPP语言</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/c5bdd8/" class="nav-link">Cpp之旅</a></li><li class="dropdown-item"><!----> <a href="/pages/279e62/" class="nav-link">Cpp专栏</a></li><li class="dropdown-item"><!----> <a href="/pages/801755/" class="nav-link">Effective_CPP</a></li><li class="dropdown-item"><!----> <a href="/pages/6b2468/" class="nav-link">muduo网络库</a></li><li class="dropdown-item"><!----> <a href="/pages/5f8c9f/" class="nav-link">Unix环境高级编程</a></li><li class="dropdown-item"><!----> <a href="/pages/3f1d21/" class="nav-link">Cpp提高编程</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="计算机基础" class="dropdown-title"><!----> <span class="title" style="display:;">计算机基础</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/7b1cb2/" class="nav-link">计算机网络</a></li><li class="dropdown-item"><!----> <a href="/pages/6048a8/" class="nav-link">操作系统</a></li><li class="dropdown-item"><!----> <a href="/pages/3b34ba/" class="nav-link">数据结构</a></li><li class="dropdown-item"><!----> <a href="/pages/412fe7/" class="nav-link">Linux</a></li><li class="dropdown-item"><!----> <a href="/pages/2dcfa1/" class="nav-link">算法</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="数据库" class="dropdown-title"><!----> <span class="title" style="display:;">数据库</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/efa3f2/" class="nav-link">基础篇</a></li><li class="dropdown-item"><!----> <a href="/pages/ccc445/" class="nav-link">MySql</a></li><li class="dropdown-item"><!----> <a href="/pages/54616e/" class="nav-link">Redis</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="嵌入式软件开发" class="dropdown-title"><!----> <span class="title" style="display:;">嵌入式软件开发</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d142c2/" class="nav-link">电子嵌入式通信协议</a></li><li class="dropdown-item"><!----> <a href="/pages/4c6bf3/" class="nav-link">深入浅出SSD</a></li><li class="dropdown-item"><!----> <a href="/pages/d3f36a/" class="nav-link">文件系统</a></li><li class="dropdown-item"><!----> <a href="/pages/e0cca7/" class="nav-link">汇编语言</a></li><li class="dropdown-item"><!----> <a href="/pages/fab2d7/" class="nav-link">STM32</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="开发日常" class="dropdown-title"><!----> <span class="title" style="display:;">开发日常</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/e472d1/" class="nav-link">随笔（持续更新）</a></li><li class="dropdown-item"><!----> <a href="/pages/71f6ae/" class="nav-link">Git知识总结</a></li><li class="dropdown-item"><!----> <a href="/pages/db6fb8/" class="nav-link">Git备忘清单</a></li><li class="dropdown-item"><!----> <a href="/pages/e1081f/" class="nav-link">Git 创建删除远程分支</a></li><li class="dropdown-item"><!----> <a href="/pages/777b8a/" class="nav-link">nvm使用小结</a></li><li class="dropdown-item"><!----> <a href="/pages/ee770e/" class="nav-link">虚拟机固定 IP 地址</a></li><li class="dropdown-item"><!----> <a href="/pages/1ab9a6/" class="nav-link">Shell 脚本学习笔记</a></li><li class="dropdown-item"><!----> <a href="/pages/411aa4/" class="nav-link">VScode 插件 CodeGeeX 使用教程</a></li><li class="dropdown-item"><!----> <a href="/pages/0d525d/" class="nav-link">KylinV10 将项目上传至 Github教程</a></li><li class="dropdown-item"><!----> <a href="/pages/907786/" class="nav-link">KylinV10 安装 MySQL 教程（可防踩雷）</a></li><li class="dropdown-item"><!----> <a href="/pages/a2d21e/" class="nav-link">kylinV10-SP1 安装 QT</a></li><li class="dropdown-item"><!----> <a href="/pages/b561cf/" class="nav-link">高并发内存池</a></li><li class="dropdown-item"><!----> <a href="/pages/6ab6d1/" class="nav-link">USBGUARD 项目编译环境配置</a></li><li class="dropdown-item"><!----> <a href="/pages/883f02/" class="nav-link">Power_Destory 项目</a></li><li class="dropdown-item"><!----> <a href="/pages/479472/" class="nav-link">U 盘清除工具编译教程</a></li><li class="dropdown-item"><!----> <a href="/pages/9c4241/" class="nav-link">个人博客代码推送教程</a></li><li class="dropdown-item"><!----> <a href="/pages/3ad765/" class="nav-link">SVN Trunk Branches的Merge操作</a></li><li class="dropdown-item"><!----> <a href="/pages/0c0ca8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端学习" class="dropdown-title"><!----> <span class="title" style="display:;">前端学习</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/99897f/" class="nav-link">HTML与CSS</a></li><li class="dropdown-item"><!----> <a href="/pages/51542d/" class="nav-link">JS学习</a></li><li class="dropdown-item"><!----> <a href="/pages/803f9d/" class="nav-link">Vue3入门</a></li><li class="dropdown-item"><!----> <a href="/pages/ca4cfb/" class="nav-link">Vue3进阶</a></li><li class="dropdown-item"><!----> <a href="/pages/50e8d3/" class="nav-link">黑马Vue3</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="MFC" class="dropdown-title"><!----> <span class="title" style="display:;">MFC</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/a4b108/" class="nav-link">MFC编程随记</a></li><li class="dropdown-item"><!----> <a href="/pages/41acbd/" class="nav-link">MFC实现ini配置文件的读取</a></li><li class="dropdown-item"><!----> <a href="/pages/951a7a/" class="nav-link">MFC实现点击列表头排序</a></li><li class="dropdown-item"><!----> <a href="/pages/a8598f/" class="nav-link">贴图法美化Button按钮</a></li><li class="dropdown-item"><!----> <a href="/pages/054516/" class="nav-link">MFC使用细节</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="闪存" class="dropdown-title"><!----> <span class="title" style="display:;">闪存</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/b925b8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li><li class="dropdown-item"><!----> <a href="/pages/28ec23/" class="nav-link">NAND Flash</a></li><li class="dropdown-item"><!----> <a href="/pages/62bf40/" class="nav-link">ARM 处理器</a></li><li class="dropdown-item"><!----> <a href="/pages/1a9374/" class="nav-link">嵌入式基础知识-存储器</a></li><li class="dropdown-item"><!----> <a href="/pages/aac5e3/" class="nav-link">闪存存储和制造技术概述</a></li><li class="dropdown-item"><!----> <a href="/pages/8f6056/" class="nav-link">芯片IO驱动力</a></li><li class="dropdown-item"><!----> <a href="/pages/d146b8/" class="nav-link">主流先进封装技术介绍</a></li><li class="dropdown-item"><!----> <a href="/pages/16f0ba/" class="nav-link">NAND Flash基础</a></li><li class="dropdown-item"><!----> <a href="/pages/90d8d0/" class="nav-link">基于PA算法的FTL引导</a></li><li class="dropdown-item"><!----> <a href="/pages/eb672b/" class="nav-link">SD逻辑擦除和物理擦除</a></li><li class="dropdown-item"><!----> <a href="/pages/747121/" class="nav-link">NAND Flash的SDR、ONFI、DDR接口</a></li><li class="dropdown-item"><!----> <a href="/pages/1eb351/" class="nav-link">【详解】Nand Flash必看知识</a></li><li class="dropdown-item"><!----> <a href="/pages/d2512a/" class="nav-link">【两万字详解】Nand Flash必看知识</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="面经" class="dropdown-title"><!----> <span class="title" style="display:;">面经</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d69946/" class="nav-link">虎牙C++技术面经</a></li><li class="dropdown-item"><!----> <a href="/pages/29251d/" class="nav-link">金山一面复习</a></li><li class="dropdown-item"><!----> <a href="/pages/c7c01f/" class="nav-link">完美世界秋招 C++ 游戏开发面经(Cpp部分)</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="其它" class="dropdown-title"><!----> <span class="title" style="display:;">其它</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/fa256e/" class="nav-link">博客搭建</a></li><li class="dropdown-item"><!----> <a href="/pages/335531/" class="nav-link">网站收藏箱</a></li></ul></div></div> <!----></nav>  <ul class="sidebar-links"><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>Cpp之旅</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/pages/c5bdd8/" class="sidebar-link">第1章 基础</a></li><li><a href="/pages/88a7db/" class="sidebar-link">第2章 用户自定义类型</a></li><li><a href="/pages/61ffe6/" class="sidebar-link">第3章 模块化</a></li><li><a href="/pages/2dfe3d/" class="sidebar-link">第4章 错误处理</a></li><li><a href="/pages/1cb324/" class="sidebar-link">第5章 类</a></li><li><a href="/pages/fae683/" class="sidebar-link">第6章 基本操作</a></li><li><a href="/pages/2cdace/" aria-current="page" class="active sidebar-link">第7章 模板</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/pages/2cdace/#_7-1-参数化类型" class="sidebar-link">7.1 参数化类型</a></li><li class="sidebar-sub-header level2"><a href="/pages/2cdace/#_7-2-受限模板参数" class="sidebar-link">7.2 受限模板参数</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/pages/2cdace/#_7-2-1-模板参数值" class="sidebar-link">7.2.1 模板参数值</a></li><li class="sidebar-sub-header level3"><a href="/pages/2cdace/#_7-2-2-模板参数推导" class="sidebar-link">7.2.2 模板参数推导</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/pages/2cdace/#_7-3-参数化操作" class="sidebar-link">7.3 参数化操作</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/pages/2cdace/#_7-4-函数对象" class="sidebar-link">7.4 函数对象</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/pages/2cdace/#_7-5-匿名函数表达式-lambda" class="sidebar-link">7.5 匿名函数表达式(lambda)</a></li><li class="sidebar-sub-header level2"><a href="/pages/2cdace/#_7-6-作用域终结函数" class="sidebar-link">7.6 作用域终结函数</a></li><li class="sidebar-sub-header level2"><a href="/pages/2cdace/#_7-7-模板机制" class="sidebar-link">7.7 模板机制</a></li><li class="sidebar-sub-header level2"><a href="/pages/2cdace/#_7-8-建议" class="sidebar-link">7.8 建议</a></li></ul></li><li><a href="/pages/619376/" class="sidebar-link">第8章 概念和泛型编程</a></li><li><a href="/pages/48ac45/" class="sidebar-link">第9章 标准库</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Cpp专栏</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Effetcive_CPP</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>muduo网络库</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Unix环境高级编程</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Cpp提高编程</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><span data-v-06225672>CPP语言</span></li><li data-v-06225672><span data-v-06225672>Cpp之旅</span></li></ul> <div class="info" data-v-06225672><div title="作者" class="author iconfont icon-touxiang" data-v-06225672><a href="javascript:;" data-v-06225672>霜晨月</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-11-24</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">第7章 模板<!----></h1> <!----> <div class="theme-vdoing-content content__default"><h1 id="cpp之旅-学习笔记-第7章-模板"><a href="#cpp之旅-学习笔记-第7章-模板" class="header-anchor">#</a> Cpp之旅（学习笔记）第7章 模板</h1> <p>模板是一个类或者一个函数，我们用一组类型或值对其进行参数化。</p> <h2 id="_7-1-参数化类型"><a href="#_7-1-参数化类型" class="header-anchor">#</a> 7.1 参数化类型</h2> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span> <span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
<span class="token keyword">class</span> <span class="token class-name">Vector</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span><span class="token operator">:</span>
    T<span class="token operator">*</span> elem<span class="token punctuation">;</span>
    <span class="token keyword">int</span> sz<span class="token punctuation">;</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token keyword">explicit</span> <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span> s<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token operator">~</span><span class="token function">Vector</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span> <span class="token keyword">delete</span><span class="token punctuation">[</span><span class="token punctuation">]</span> elem<span class="token punctuation">;</span><span class="token punctuation">}</span>
    T<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span><span class="token punctuation">;</span>				<span class="token comment">//对于非常量的Vector</span>
    <span class="token keyword">const</span> T<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span> <span class="token keyword">const</span><span class="token punctuation">;</span> 	<span class="token comment">//对于常量Vector</span>
    <span class="token keyword">int</span> <span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">const</span> <span class="token punctuation">{</span><span class="token keyword">return</span> sz<span class="token punctuation">;</span><span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><p>前缀<code>template &lt;typename T&gt;</code>指明T是该声明的形参。在引出类型参数时，使用class和使用typename是等价的，在旧式代码中经常出现将<code>template &lt;class T&gt;</code>作为前缀。</p> <p>成员函数的定义方式与之类似：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
<span class="token class-name">Vector</span><span class="token operator">&lt;</span>T<span class="token operator">&gt;</span><span class="token double-colon punctuation">::</span><span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span> s<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>s <span class="token operator">&lt;</span> <span class="token number">0</span><span class="token punctuation">)</span>
        <span class="token keyword">throw</span> length_error<span class="token punctuation">{</span><span class="token string">&quot;Vector constructor: negative size&quot;</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
    elem <span class="token operator">=</span> <span class="token keyword">new</span> T<span class="token punctuation">[</span>s<span class="token punctuation">]</span><span class="token punctuation">;</span>
    sz <span class="token operator">=</span> s<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
<span class="token keyword">const</span> T<span class="token operator">&amp;</span> Vector<span class="token operator">&lt;</span>T<span class="token operator">&gt;</span><span class="token double-colon punctuation">::</span><span class="token keyword">operator</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span> <span class="token keyword">const</span>
<span class="token punctuation">{</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>i <span class="token operator">&lt;</span> <span class="token number">0</span> <span class="token operator">||</span> <span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&lt;=</span> i<span class="token punctuation">)</span>
        <span class="token keyword">throw</span> out_of_range<span class="token punctuation">{</span><span class="token string">&quot;Vector::operator[]&quot;</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> elem<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><p>可以用如下方式声明动态数组Vector：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code>Vector<span class="token operator">&lt;</span><span class="token keyword">char</span><span class="token operator">&gt;</span> <span class="token function">vc</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 200个字符组成的动态数组</span>
Vector<span class="token operator">&lt;</span>string<span class="token operator">&gt;</span> <span class="token function">vs</span><span class="token punctuation">(</span><span class="token number">17</span><span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 17个字符串组成的动态数组</span>
Vector<span class="token operator">&lt;</span>list<span class="token operator">&lt;</span><span class="token keyword">int</span><span class="token operator">&gt;&gt;</span> <span class="token function">vli</span><span class="token punctuation">(</span><span class="token number">45</span><span class="token punctuation">)</span><span class="token punctuation">;</span>	<span class="token comment">// 45个整数链表组成的动态数组</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>为了让Vector支持范围for循环，需要为之定义适当的begin()和end()函数：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
T<span class="token operator">*</span> <span class="token function">begin</span><span class="token punctuation">(</span>Vector<span class="token operator">&lt;</span>T<span class="token operator">&gt;</span><span class="token operator">&amp;</span> x<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token operator">&amp;</span>x<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>			<span class="token comment">// 指向第一个元素，或者指向末尾元素后面的一个位置</span>
<span class="token punctuation">}</span>
<span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
T<span class="token operator">*</span> <span class="token function">end</span><span class="token punctuation">(</span>Vector<span class="token operator">&lt;</span>T<span class="token operator">&gt;</span><span class="token operator">&amp;</span> x<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token operator">&amp;</span>x<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">+</span>x<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>	<span class="token comment">// 指向末尾元素后面的一个位置</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><ul><li>模板是一种编译时的机制，因此与“手工编码”相比，它并不会产生任何额外的运行时开销。</li> <li>模板加上一系列模板参数被统称为实例化或者特例化。在编译过程中进行实例化时，每个实例都会生成一份代码。</li></ul> <h2 id="_7-2-受限模板参数"><a href="#_7-2-受限模板参数" class="header-anchor">#</a> 7.2 受限模板参数</h2> <p>Vector的模板参数仅仅是一个typename还不够，还需要指定Element满足特定需求才能成为其元素：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span>Element T<span class="token operator">&gt;</span>
<span class="token keyword">class</span> <span class="token class-name">Vector</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span><span class="token operator">:</span>
    T<span class="token operator">*</span> elem<span class="token punctuation">;</span>
    <span class="token keyword">int</span> sz<span class="token punctuation">;</span>
    <span class="token comment">// ...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>这里，<code>template&lt;Element T&gt;</code>Element是一个谓词，用于检查T是否满足Vector需要的特性。</p> <p>这种谓词叫做概念。在模板参数中指定一个概念，这叫作受限模板参数，拥有这种参数的模板叫作受限模板。</p> <h3 id="_7-2-1-模板参数值"><a href="#_7-2-1-模板参数值" class="header-anchor">#</a> 7.2.1 模板参数值</h3> <p>除了类型参数以外，模板还支持值作为参数。</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token punctuation">,</span> <span class="token keyword">int</span> N<span class="token operator">&gt;</span>
<span class="token keyword">struct</span> <span class="token class-name">Buffer</span><span class="token punctuation">{</span>
    <span class="token keyword">constexpr</span> <span class="token keyword">int</span> <span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token keyword">return</span> N<span class="token punctuation">;</span><span class="token punctuation">}</span>
    T elem<span class="token punctuation">[</span>N<span class="token punctuation">]</span><span class="token punctuation">;</span>
    <span class="token comment">// ...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>值参数在很多环境中都有用。例如：Buffer允许我们创建任意尺寸的缓冲区而不需要使用动态内存分配：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code>Buffer<span class="token operator">&lt;</span><span class="token keyword">char</span><span class="token punctuation">,</span><span class="token number">1024</span><span class="token operator">&gt;</span> glob<span class="token punctuation">;</span>		<span class="token comment">// 静态分配的全局char缓冲区</span>
<span class="token keyword">void</span> <span class="token function">fct</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    Buffer<span class="token operator">&lt;</span><span class="token keyword">int</span><span class="token punctuation">,</span><span class="token number">10</span><span class="token operator">&gt;</span> buf<span class="token punctuation">;</span>		<span class="token comment">// 栈上分配的本地int缓冲区</span>
    <span class="token comment">// ...</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>但是，字符串字面量不可以作为模板值参数。但我们可以使用存放字符的数组来表示字符串：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">char</span><span class="token operator">*</span> s<span class="token operator">&gt;</span>
<span class="token keyword">void</span> <span class="token function">outs</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span> 
    cout <span class="token operator">&lt;&lt;</span> s<span class="token punctuation">;</span> 
<span class="token punctuation">}</span>

<span class="token keyword">char</span> arr<span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string">&quot;Werid workaround&quot;</span><span class="token punctuation">;</span>
<span class="token keyword">void</span> <span class="token function">use</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    outs <span class="token operator">&lt;</span><span class="token string">&quot;straightforward use&quot;</span><span class="token operator">&gt;</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 到目前为止，这样不可行</span>
    <span class="token generic-function"><span class="token function">outs</span><span class="token generic class-name"><span class="token operator">&lt;</span>arr<span class="token operator">&gt;</span></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>						<span class="token comment">// 诡异的间接解决方案</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><h3 id="_7-2-2-模板参数推导"><a href="#_7-2-2-模板参数推导" class="header-anchor">#</a> 7.2.2 模板参数推导</h3> <p>指定模板参数类型显得有些冗长，考虑使用标准库模板pair：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code>pair<span class="token operator">&lt;</span><span class="token keyword">int</span><span class="token punctuation">,</span><span class="token keyword">double</span><span class="token operator">&gt;</span> p <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">5.2</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token comment">// 等价于</span>
pair p <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">5.2</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>可以使用s后缀把字符串变成一个正确的string</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
<span class="token keyword">class</span> <span class="token class-name">Vector</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">Vector</span><span class="token punctuation">(</span>initializer_list<span class="token operator">&lt;</span>T<span class="token operator">&gt;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 初始化列表构造函数</span>
    <span class="token comment">// ...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

Vector<span class="token operator">&lt;</span>string<span class="token operator">&gt;</span> vs <span class="token punctuation">{</span><span class="token string">&quot;Hello&quot;</span><span class="token punctuation">,</span> <span class="token string">&quot;World&quot;</span><span class="token punctuation">}</span><span class="token punctuation">;</span>	<span class="token comment">// 可行：Vector&lt;string&gt;</span>
Vector vs1 <span class="token punctuation">{</span><span class="token string">&quot;Hello&quot;</span>s<span class="token punctuation">,</span> <span class="token string">&quot;World&quot;</span>s<span class="token punctuation">}</span><span class="token punctuation">;</span>		<span class="token comment">// 可行：推导为Vector&lt;string&gt;</span>
Vector vs2 <span class="token punctuation">{</span><span class="token string">&quot;Hello&quot;</span>s<span class="token punctuation">,</span> <span class="token string">&quot;World&quot;</span><span class="token punctuation">}</span><span class="token punctuation">;</span>			<span class="token comment">// 错误：初始化列表中的数据类型不一致</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><h2 id="_7-3-参数化操作"><a href="#_7-3-参数化操作" class="header-anchor">#</a> 7.3 参数化操作</h2> <p>模板还被广泛用于参数化标准库中的类型与算法。</p> <p>要想表达将操作用类型或者值来参数化，有三种方法：</p> <ul><li>模板函数。</li> <li>函数对象：对象可以携带数据，并且以函数的形式调用。</li> <li>匿名函数表达式：函数对象的简略记法。</li></ul> <p><strong>==模板函数可以是成员函数，但不能是virtual函数。编译器不可能知道模板的所有实例，所以不可能像函数一样被调用。==</strong></p> <h3 id="_7-4-函数对象"><a href="#_7-4-函数对象" class="header-anchor">#</a> 7.4 函数对象</h3> <p>一种特别有用的模板叫作函数对象（有时也被称为仿函数），它可以用来定义对象，该对象可以像函数一样被调用。</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
<span class="token keyword">class</span> <span class="token class-name">Less_than</span><span class="token punctuation">{</span>
    <span class="token keyword">const</span> T val<span class="token punctuation">;</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">Less_than</span><span class="token punctuation">(</span><span class="token keyword">const</span> T<span class="token operator">&amp;</span> v<span class="token punctuation">)</span><span class="token operator">:</span><span class="token function">val</span><span class="token punctuation">(</span>v<span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    <span class="token keyword">bool</span> <span class="token keyword">operator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token keyword">const</span> T<span class="token operator">&amp;</span> x<span class="token punctuation">)</span> <span class="token keyword">const</span> <span class="token punctuation">{</span><span class="token keyword">return</span> x <span class="token operator">&lt;</span> val<span class="token punctuation">;</span><span class="token punctuation">}</span>	<span class="token comment">//函数调用操作符</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>名叫operator()的函数实现了应用操作符()，这个操作符又可被称作“函数调用操作符”“调用操作符”。</p> <h2 id="_7-5-匿名函数表达式-lambda"><a href="#_7-5-匿名函数表达式-lambda" class="header-anchor">#</a> 7.5 匿名函数表达式(lambda)</h2> <p>匿名函数表达式（lambda）</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token punctuation">[</span><span class="token operator">&amp;</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> a<span class="token punctuation">)</span><span class="token punctuation">{</span> <span class="token keyword">return</span> a <span class="token operator">&lt;</span> x<span class="token punctuation">;</span> <span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>[&amp;]是匿名函数的捕获列表，它指定了函数体内所有局部变量可以以引用的形式被访问。</strong></p> <ul><li>只捕获x这一个变量，使用[&amp;x]；</li> <li>生成x的一份拷贝，使用[x]；</li> <li>什么都不捕获，使用[]；</li> <li>以引用的方式捕获所有局部变量，使用[&amp;]；</li> <li>以值的方式捕获所有局部变量，使用[=]；</li> <li>如果成员函数中定义匿名函数，使用[this]来捕获当前对象；</li> <li>如果成员函数中定义匿名函数，可以使用[*this]捕获当前对象的拷贝。</li></ul> <h2 id="_7-6-作用域终结函数"><a href="#_7-6-作用域终结函数" class="header-anchor">#</a> 7.6 作用域终结函数</h2> <p>析构函数提供了一种通用的方案，用于在作用域结束时隐式清除所有使用过的对象RAII，但如果需要进行的清理涉及多个对象，或者涉及不含析构函数的对象，可以定义一个finally()函数，它在作用域结束时执行：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">void</span> <span class="token function">old_style</span><span class="token punctuation">(</span><span class="token keyword">int</span> n<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    <span class="token keyword">void</span> <span class="token operator">*</span>p <span class="token operator">=</span> <span class="token function">malloc</span><span class="token punctuation">(</span>n<span class="token operator">*</span> <span class="token keyword">sizeof</span><span class="token punctuation">(</span><span class="token keyword">int</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">auto</span> act <span class="token operator">=</span> <span class="token function">finally</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token operator">&amp;</span><span class="token punctuation">]</span><span class="token punctuation">{</span><span class="token function">free</span><span class="token punctuation">(</span>p<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>	<span class="token comment">// 作用域结束时调用该匿名函数</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>实现finally()函数的方法：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">class</span> <span class="token class-name">F</span><span class="token operator">&gt;</span>
<span class="token punctuation">[</span><span class="token punctuation">[</span>nodiscard<span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token keyword">auto</span> <span class="token function">finally</span><span class="token punctuation">(</span>F f<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    <span class="token keyword">return</span> Final_action<span class="token punctuation">{</span>f<span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>这里使用了[[nodiscard]]属性修饰，确保用户不会忘记保存所生成的返回值Final_action，因为正常完成功能必须保存它。</p> <p>用来提供析构函数的类Final_action可以写成下面这样：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">class</span> <span class="token class-name">F</span><span class="token operator">&gt;</span>
<span class="token keyword">struct</span> <span class="token class-name">Final_action</span><span class="token punctuation">{</span>
    <span class="token keyword">explicit</span> <span class="token function">Final_action</span><span class="token punctuation">(</span>F f<span class="token punctuation">)</span><span class="token operator">:</span><span class="token function">act</span><span class="token punctuation">(</span>f<span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    <span class="token operator">~</span><span class="token function">Final_action</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token function">act</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">}</span>
    F act<span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><h2 id="_7-7-模板机制"><a href="#_7-7-模板机制" class="header-anchor">#</a> 7.7 模板机制</h2> <ul><li>依赖类型的值：参数模板</li> <li>类型与模板的别名：别名模板</li> <li>编译时选择机制：if constexpr</li> <li>编译时查询值与表达式属性的机制：requires表达式</li></ul> <h2 id="_7-8-建议"><a href="#_7-8-建议" class="header-anchor">#</a> 7.8 建议</h2> <ol><li>用模板来表达那些可以用于多种参数类型的算法；</li> <li>用模板实现容器；</li> <li>用模板提升代码的抽象层次；</li> <li>让构造函数或函数模板推断出类模板实参类型；</li> <li>把函数对象作为算法的参数；</li> <li>如果简单的函数对象只在某处使用一次，不妨使用匿名函数；</li> <li>不能把虚函数成员定义成模板成员函数；</li> <li>使用finally()为不带析构函数且需要“清理操作”的类型提供RAII；</li> <li>利用模板别名来简化符号并隐藏实现细节；</li> <li>使用if constexpr条件编译提供替代实现，不会存在运行时开销；</li></ol></div></div> <!----> <div class="page-edit"><!----> <!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2024/6/3 14:54:44</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/fae683/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">第6章 基本操作</div></a> <a href="/pages/619376/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">第8章 概念和泛型编程</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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